Or magenta treated with a bleaching-agent in just sufficient quantity to decolorise it is invisible when used for writing.    From Wordnik.com.  [Master Tales of Mystery, Volume 3] Reference

A is molecular formula C8H10 does not decolorise bromine water but when refluxed with aq, acidified KMnO4 the latter decolorise forming compound B with C7H6O2.    From Wordnik.com.  [Yahoo! Answers: Latest Questions] Reference